In order to control insects that may be harmful or otherwise undesirable to man, much attention has been directed to improvements in methods for delivering chemical pest control agents.
A special insecticide dispenser is known from U.S. Pat. No. 4,639,393 disclosing a laminated dispenser with two outer wall elements enclosing an inner layer containing a pest controlling agent. The pest controlling agent is able to migrate through the outer layers for a controlled release of the agent to the surface of the dispenser. Such a dispenser may be used for example for wall paper, floor coverings or tarpaulins.
It is well known that insecticides when exposed to ultra violet (UV radiation) are degraded through the UV induced chemical reactions. The dispenser disclosed in U.S. Pat. No. 4,639,393 takes into account UV protection of the pesticidal agent in the internal reservoir by incorporation of an ultra violet light screening agent in the wall portion of the dispenser.
However, the disclosure in U.S. Pat. No. 4,639,393 does not take into account any protection of the pest controlling agent after migration to the outer surface of the wall element Especially in tropic regions, UV radiation is very strong and the insecticide that has migrated to the surface of the laminate may disintegrate at a rate so high that no efficient insecticidal effect may be achieved. Therefore, the laminated dispenser disclosed in the above mentioned patent is primarily suited for indoor use or generally where high levels of UV radiation is avoided. In connection with applications where a high intensity of UV radiation is given, the insecticide release from a dispenser as disclosed in U.S. Pat. No. 4,639,393 has to be fast such that a suitable active level of insecticide, or alternatively an insect attractant, can be maintained on the surface. However, this limits the lifetime of the dispenser, because the insecticide reservoir is emptied after relatively short time, for example a few weeks.
It is the purpose of the invention to improve existing dispensers such that they are more suitable for application in outdoor environments where the dispenser is exposed to primarily high level UV radiation.